1. Field of the Invention
The embodiments of the invention generally relate to a slit valve door for sealing substrate passages in vacuum processing systems.
2. Background of the Related Art
Thin film transistors (TFT) are commonly used for active matrix displays such as computer and television monitors, cell phone displays, personal digital assistants (PDAs), and an increasing number of other devices. Generally, flat panels comprise two glass plates having a layer of liquid crystal materials sandwiched therebetween. At least one of the glass plates includes one conductive film disposed thereon that is coupled to a power source. Power, supplied to the conductive film from the power source, changes the orientation of the crystal material, creating a pattern display.
With the marketplace's acceptance of flat panel technology, the demand for larger displays, increased production and lower manufacturing costs have driven equipment manufacturers to develop new systems that accommodate larger size glass substrates for flat panel display fabricators. Current glass processing equipment is generally configured to accommodate substrates up to about one square meter. Processing equipment configured to accommodate substrate sizes up to and exceeding four square meters is envisioned in the immediate future.
Glass substrate processing is typically performed in a cluster tool by subjecting a substrate to a plurality of sequential processes to create devices, conductors, and insulators on the substrate. Each of these processes is generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, the cluster tool includes a number of process chambers coupled to a central transfer chamber. A robot is housed in the transfer chamber to facilitate transfer of the substrate between the process chambers and a load lock chamber. The load lock chamber allows substrates to be transferred between the vacuum environment of the cluster tool and an ambient environment of a factory interface. Such cluster tools for glass substrate processing are available from AKT, Inc., a wholly-owned subsidiary of Applied Materials, Inc., of Santa Clara, Calif.
As the substrate size for manufacturing flat panel display grows, the manufacturing equipment for these substrates becomes larger in size as well. Accordingly, the door or gate that isolates one vacuum chamber (or load lock) from another has become larger, or, specifically longer since the slot opening between the two chambers has to become wider to accommodate the large width of the substrate passing through the slot opening. The increasing length of the door poses a technical challenge for obtaining a good isolation seal between the two chambers, which is maintained by an elastomer seal disposed around the slot opening between the door and a chamber wall.
FIG. 1A depicts a partial sectional view of a substrate passage 108 formed through a chamber body 106 and selectively sealed by a conventional slit valve door 110. Conventional slit valve doors are typically comprised of a flat member of aluminum having a long lateral span. A closing force is applied toward the center of the door 110 by brackets 102 attached, as shown in FIGS. 1A-B, to a stiff rotating shaft 104. The door 110 is rotated between a position sealing the passage 108 (as shown in FIG. 1A) and a position clear of the passage 108 by an actuator 118 coupled to the shaft 104. A seal 116 is disposed between the door 110 and chamber body 106.
The force required to load the seal 116 in order to obtain good chamber isolation is high. The high load applied near the center of the door 110 results in a high loading force approximate the center of the door 110 and a substantially lower sealing force near the ends of the door, as depicted by force arrows 112. The shaft 104 may deflect while under load as shown by the phantom shaft 114, as the door 110 has a long span between its bearing supports 114 disposed in the walls of the chamber body 106 and the brackets 102 coupled to the center of the door 110. Deflection of the shaft 114 while the door 110 is in a closed position further aggravates the low loading condition of the seal at the ends of the door. The low sealing force at the edge of the door may lead to undesirable leakage through the passage 108.
In order to provide a stiffer door for more uniform seal loading, the door and/or the shaft may be fabricated from thicker materials or materials having higher modulus. However, this approach increases the cost of the load lock chamber, as high strength materials are typically expensive, and a larger load lock chamber may be required to accommodate the larger, high strength door with adequate clearance during operation. A larger load lock chamber is undesirable due to the increased material and manufacturing costs of the chamber itself, along with increased pump capacity required to pump down the larger load lock volume. Moreover, increased load lock volume typically requires increased pump time which has an adverse affect on system throughput.
Therefore, there is a need for an improved slit valve door for sealing a substrate transfer passage.